Wide bandwidth fiber raman amplifier

Abstract

A method of Raman amplification comprising the step of effecting a plurality of pump wavelengths on a Raman-active transmission medium transmitting counter-propagating signal wavelengths, wherein at least one of said pump wavelengths are interleaved between said signal wavelengths.

Description

FIELD OF THE INVENTIONThis invention pertains to Raman amplifiers and, more particularly, to Raman amplifiers having a bandwidth which exceeds the peak Raman Stokes gain shift of the transmission medium with which the Raman amplifier is utilized.BACKGROUND OF THE INVENTIONOptical fiber technology is currently utilized in communications systems to transfer information, e.g., voice signals and data signals, over long distances as optical signals. Over such long distances, however, the strength and quality of a transmitted optical signal diminishes. Accordingly, techniques have been developed to regenerate or amplify optical signals as they propagate along an optical fiber.One well-known amplifying technique exploits an effect called Raman scattering to amplify an incoming information-bearing optical signal (referred to herein as a "signal wavelength"). Raman scattering describes the interaction of light with molecular vibrations of the material through which the light propagates (refe...

AI Technical Summary

Benefits of technology

In accordance with the present invention, the amplification bandwidth of a Raman amplifier is expanded by interleaving narrow pump wavelengths between signal wavelengths, thereby avoiding interaction between the signal wavelengths and the BRS of the interleaved pump wavelengths. The line width of the pump signals are narrow enough (e.g., less than 1 GHz) compared to the wavelength spacing of the signal wavelengths (e.g., as low as 25 GHz) so that the BRS of the interleaved pump wavelengths is readily distinguishable from signal wavelengths and can be efficiently filtered out.

Problems solved by technology

Over such long distances, however, the strength and quality of a transmitted optical signal diminishes.

Co-propagating pumps may be used, although a counter-propagation pump scheme reduces polarization sensitivity and cross talk between wavelength division multiplexed (WDM) channels.

Despite multiple pump configurations, prior art Raman amplifiers are nevertheless limited in bandwidth, which in turn limits the capacity of WDM systems.

More specifically, because the effective Raman gain tails off at about 125 nm from the pump wavelength, signal wavelengths beyond this point are not effectively amplified.

Although the pump and signal wavelengths can be easily separated by filtering in a counter-propagating scheme, the BRS from the pump wavelengths, which propagates in the direction of the signals, is not easily filtered.

The BRS from the pump wavelength at point A is affected by the Raman gain of the lower pump wavelengths, thus introducing undesired noise into the signal wavelengths near point A (FIG. 2).

Thus, BRS both decreases the Raman amplification of the adjacent signals by depleting the pump wavelengths' power, and diminishes signal quality by introducing noise and cross-talk between the channels.

The two side bands may also introduce undesired noise into the signal wavelengths.

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